The piston engine must limit the combustion gas expansion by venting high pressure gases to avoid negative work. The resulting hot and noisy exhaust release is expected with this type of engine.A practical engine cycle and mechanism have been developed that extracts more work as the gases are expanded down to atmospheric pressure. The mechanism is the Migrating Combustion Chamber (MCC) engine and operates on a new cycle at an increased efficiency with a quiet, cool, zero positive pressure blow down. The typical muffler system is therefore eliminated. The required 3 to 3.5 ratio of expansion volume to swept intake volume, rapid large area porting, and low pumping and frictional losses are achieved by the use of an additional expansion chamber inherent in the MCC engine design.Operational characteristics and performance data are presented on prototype engines up to 5 HP and compared against commercially available counterpart piston engines.